Crowdsourcing has been used in the cultural heritage domain for a variety of tasks. One of them is generation of descriptive metadata for digital archives. Gamification offers citizens a more entertaining way to interact with digital collections and generate useful metadata as a side effect of gameplay. The rise of social gaming on Facebook in recent years opens new horizons for cultural heritage institutions to leverage the capabilities of social networking platforms and to gain immediate access to millions of potential contributors. In this work, we explore the integration of social networks with crowdsourcing games for generating archival metadata. We studied crowdsourcing, gamification and social dynamics from the perspective of cultural heritage and combine their features in a metadata game prototype on the Facebook platform. We tested our prototype and evaluate its results by analysing participation, contribution and player feedback. The two-week testing phase showed promising results in terms of user engagement and produced metadata: almost 3000 tags were added, 90% of which were valid dictionary terms. We conclude that deploying metadata games on social networking platforms is a feasible method for digital archives to harness human intelligence from large shared spaces.